feat: encrypted room search via local cache scan

No Matrix web client supports E2EE message search server-side — the
homeserver only sees ciphertext. This is the same approach FluffyChat
takes: scan locally decrypted events already in the live timeline.

Changes:
- useLocalMessageSearch: searches getLiveTimeline().getEvents() in
  encrypted rooms using decrypted content (getContent(), not event.content)
- MessageSearch: runs client-side search in parallel with server search,
  shows results in a dedicated 'Encrypted Rooms' section with clear notice
  about scope (only cached/recently viewed messages)
- Encryption notice shown when encrypted rooms are in scope — explains
  why results may be missing and what to do
- Server result limit raised from 20 → 50

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/message-search/MessageSearch.tsx

@@ -19,6 +19,7 @@ import { useRooms } from '../../state/hooks/roomList';
 import { allRoomsAtom } from '../../state/room-list/roomList';
 import { mDirectAtom } from '../../state/mDirectList';
 import { MessageSearchParams, useMessageSearch } from './useMessageSearch';
+import { useLocalMessageSearch } from './useLocalMessageSearch';
 import { SearchResultGroup } from './SearchResultGroup';
 import { SearchInput } from './SearchInput';
 import { SearchFilters } from './SearchFilters';
@@ -95,6 +96,19 @@ export function MessageSearch({
   }, [searchPathSearchParams, searchParamRooms, searchParamsSenders, rooms, senders]);
 
   const searchMessages = useMessageSearch(msgSearchParams);
+  const searchLocalMessages = useLocalMessageSearch();
+
+  // The rooms actually in scope for this search (mirrors server-side logic)
+  const localSearchRooms = useMemo(
+    () => msgSearchParams.rooms ?? (searchPathSearchParams.global === 'true' ? allRooms : rooms),
+    [msgSearchParams.rooms, searchPathSearchParams.global, allRooms, rooms],
+  );
+
+  // Run synchronous client-side search over encrypted rooms immediately
+  const localResult = useMemo(() => {
+    if (!msgSearchParams.term) return null;
+    return searchLocalMessages(localSearchRooms, msgSearchParams.term);
+  }, [searchLocalMessages, localSearchRooms, msgSearchParams.term]);
 
   const { status, data, error, fetchNextPage, hasNextPage, isFetchingNextPage } = useInfiniteQuery({
     enabled: !!msgSearchParams.term,
@@ -237,16 +251,36 @@ export function MessageSearch({
       )}
 
       {msgSearchParams.term && groups.length === 0 && status === 'success' && (
-        <Box
-          className={ContainerColor({ variant: 'Warning' })}
-          style={{ padding: config.space.S300, borderRadius: config.radii.R400 }}
-          alignItems="Center"
-          gap="200"
-        >
-          <Icon size="200" src={Icons.Info} />
-          <Text>
-            No results found for <b>{`"${msgSearchParams.term}"`}</b>
-          </Text>
+        <Box direction="Column" gap="200">
+          <Box
+            className={ContainerColor({ variant: 'Warning' })}
+            style={{ padding: config.space.S300, borderRadius: config.radii.R400 }}
+            alignItems="Center"
+            gap="200"
+          >
+            <Icon size="200" src={Icons.Info} />
+            <Text>
+              No results found for <b>{`"${msgSearchParams.term}"`}</b>
+            </Text>
+          </Box>
+          {localResult &&
+            localResult.encryptedRoomsCount > 0 &&
+            localResult.groups.length === 0 && (
+              <Box
+                className={ContainerColor({ variant: 'Surface' })}
+                style={{ padding: config.space.S300, borderRadius: config.radii.R400 }}
+                alignItems="Center"
+                gap="200"
+              >
+                <Icon size="200" src={Icons.Lock} />
+                <Text size="T300" priority="300">
+                  {`${localResult.encryptedRoomsCount} encrypted room${localResult.encryptedRoomsCount !== 1 ? 's' : ''} in scope — the server cannot search E2EE messages. `}
+                  {localResult.searchedRoomsCount > 0
+                    ? `No matches found in your locally cached messages from ${localResult.searchedRoomsCount} room${localResult.searchedRoomsCount !== 1 ? 's' : ''}.`
+                    : `Open those rooms to cache messages locally, then search again.`}
+                </Text>
+              </Box>
+            )}
         </Box>
       )}
 
@@ -259,6 +293,23 @@ export function MessageSearch({
         </Box>
       )}
 
+      {msgSearchParams.term &&
+        localResult &&
+        localResult.encryptedRoomsCount > 0 &&
+        vItems.length > 0 && (
+          <Box
+            className={ContainerColor({ variant: 'Surface' })}
+            style={{ padding: config.space.S300, borderRadius: config.radii.R400 }}
+            alignItems="Center"
+            gap="200"
+          >
+            <Icon size="200" src={Icons.Lock} />
+            <Text size="T300" priority="300">
+              {`${localResult.encryptedRoomsCount} encrypted room${localResult.encryptedRoomsCount !== 1 ? 's' : ''} in scope — server results are from unencrypted rooms only. Encrypted room results appear below from your local cache.`}
+            </Text>
+          </Box>
+        )}
+
       {vItems.length > 0 && (
         <Box direction="Column" gap="300">
           <Box direction="Column" gap="200">
@@ -307,6 +358,41 @@ export function MessageSearch({
         </Box>
       )}
 
+      {localResult && localResult.groups.length > 0 && (
+        <Box direction="Column" gap="300">
+          <Box direction="Column" gap="200">
+            <Box alignItems="Center" gap="200">
+              <Icon size="200" src={Icons.Lock} />
+              <Text size="H5">Encrypted Rooms</Text>
+            </Box>
+            <Text size="T300" priority="300">
+              {`Showing locally cached messages from ${localResult.searchedRoomsCount} encrypted room${localResult.searchedRoomsCount !== 1 ? 's' : ''}. Only recently viewed messages are available.`}
+            </Text>
+            <Line size="300" variant="Surface" />
+          </Box>
+          <Box direction="Column" gap="300">
+            {localResult.groups.map((group) => {
+              const groupRoom = mx.getRoom(group.roomId);
+              if (!groupRoom) return null;
+              return (
+                <SearchResultGroup
+                  key={group.roomId}
+                  room={groupRoom}
+                  highlights={[msgSearchParams.term ?? '']}
+                  items={group.items}
+                  mediaAutoLoad={mediaAutoLoad}
+                  urlPreview={urlPreview}
+                  onOpen={navigateRoom}
+                  legacyUsernameColor={legacyUsernameColor || mDirects.has(groupRoom.roomId)}
+                  hour24Clock={hour24Clock}
+                  dateFormatString={dateFormatString}
+                />
+              );
+            })}
+          </Box>
+        </Box>
+      )}
+
       {error && (
         <Box
           className={ContainerColor({ variant: 'Critical' })}

src/app/features/message-search/useLocalMessageSearch.ts

@@ -0,0 +1,107 @@
+import { EventType } from 'matrix-js-sdk';
+import { useCallback } from 'react';
+import { useMatrixClient } from '../../hooks/useMatrixClient';
+import { ResultGroup, ResultItem } from './useMessageSearch';
+
+export type LocalSearchResult = {
+  groups: ResultGroup[];
+  /** How many rooms in scope are encrypted */
+  encryptedRoomsCount: number;
+  /** How many of those had locally cached events to scan */
+  searchedRoomsCount: number;
+};
+
+/**
+ * Client-side full-text search over locally cached events in encrypted rooms.
+ * The homeserver cannot search E2EE message content, so we scan whatever the
+ * client has already received and decrypted in memory.
+ *
+ * Limitation: only messages present in the live timeline window are covered.
+ * Rooms that haven't been opened yet will return no results.
+ */
+export const useLocalMessageSearch = () => {
+  const mx = useMatrixClient();
+
+  const search = useCallback(
+    (roomIds: string[], term: string): LocalSearchResult => {
+      const trimmedTerm = term.trim();
+      if (!trimmedTerm) {
+        return { groups: [], encryptedRoomsCount: 0, searchedRoomsCount: 0 };
+      }
+
+      const termLower = trimmedTerm.toLowerCase();
+      const groups: ResultGroup[] = [];
+      let encryptedRoomsCount = 0;
+      let searchedRoomsCount = 0;
+
+      for (const roomId of roomIds) {
+        const room = mx.getRoom(roomId);
+        if (!room) continue;
+
+        const isEncrypted = !!room.currentState.getStateEvents(EventType.RoomEncryption, '');
+        if (!isEncrypted) continue;
+
+        encryptedRoomsCount += 1;
+
+        const events = room.getLiveTimeline().getEvents();
+        if (events.length === 0) continue;
+
+        searchedRoomsCount += 1;
+
+        const items: ResultItem[] = [];
+
+        for (let i = 0; i < events.length; i += 1) {
+          const event = events[i];
+
+          if (event.getType() !== EventType.RoomMessage) continue;
+          if (event.isDecryptionFailure()) continue;
+          if (event.isRedacted()) continue;
+
+          // getContent() returns decrypted plaintext regardless of encryption
+          const content = event.getContent();
+          const body = (content.body as string | undefined) ?? '';
+          const formattedBody = (content.formatted_body as string | undefined) ?? '';
+
+          if (
+            !body.toLowerCase().includes(termLower) &&
+            !formattedBody.toLowerCase().includes(termLower)
+          )
+            continue;
+
+          // Build a synthetic IEventWithRoomId using decrypted content so the
+          // existing SearchResultGroup renderer works without modification.
+          const syntheticEvent = {
+            room_id: roomId,
+            event_id: event.getId() ?? '',
+            type: event.getType(),
+            sender: event.getSender() ?? '',
+            origin_server_ts: event.getTs(),
+            content,
+            unsigned: event.getUnsigned(),
+          };
+
+          items.push({
+            rank: 0,
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+            event: syntheticEvent as any,
+            context: {
+              events_before: [],
+              events_after: [],
+              profile_info: {},
+            },
+          });
+        }
+
+        if (items.length > 0) {
+          items.sort((a, b) => (b.event.origin_server_ts ?? 0) - (a.event.origin_server_ts ?? 0));
+          groups.push({ roomId, items });
+        }
+      }
+
+      return { groups, encryptedRoomsCount, searchedRoomsCount };
+    },
+    [mx],
+  );
+
+  return search;
+};

src/app/features/message-search/useMessageSearch.ts

@@ -80,7 +80,7 @@ export const useMessageSearch = (params: MessageSearchParams) => {
           highlights: [],
           groups: [],
         };
-      const limit = 20;
+      const limit = 50;
 
       const requestBody: ISearchRequestBody = {
         search_categories: {